Method and apparatus for driving flow control electromagnetic proportional control valve

ABSTRACT

In a method for driving a solenoid proportional control valve ( 44 ) used for flow rate control of a common rail system pump adapted to regulate flow rate by regulating the duty ratio of a pulse voltage applied to a solenoid coil (F) of a solenoid ( 44 E), when an operating condition liable to cause hysteresis in the operation of the solenoid proportional control valve ( 44 ) is present, the peak value or pulse width of the pulse voltage is temporarily increased to instantaneously boost the driving force of the solenoid ( 44 E), thereby ensuring smooth operation of a piston ( 44 C) and stabilizing the flow rate control.

TECHNICAL FIELD

The present invention relates to a method and an apparatus for driving asolenoid proportional control valve utilized for flow rate control.

BACKGROUND ART

Solenoid proportional control valves for flow rate control have longbeen used to control the flow rate of liquid fuels and other fluids invarious systems. Consider, for example, the fuel injection system thataccumulates high-pressure fuel in a common rail and injects thehigh-pressure fuel through injectors into the cylinders of an internalcombustion engine. The pump unit provided for feeding the high-pressurefuel into the common rail in this system includes a feed pump forfeeding fuel from a fuel tank and is configured to pressurize the fuelsupplied by the feed pump using a high-pressure plunger and to feed thehighly pressurized fuel into the common rail. The fuel supplied from thefeed pump to the high-pressure plunger is controlled to an amountappropriate for the instantaneous operating condition of the engine by asolenoid proportional control valve.

The solenoid proportional control valve used for this purpose isequipped with a spring-biased piston slidably accommodated in a cylinderand a solenoid for positioning the piston against the biasing force ofthe spring. The positional relationship between the piston and cylinderis controlled in proportion to the magnitude of the driving currentsupplied to the solenoid to regulate the open area of a fuel passageport formed in the cylinder and thus regulate the flow rate of fuelpassing through the solenoid proportional control valve.

Ordinarily, the coil of the solenoid of the so-configured solenoidproportional control valve is supplied with a constant frequency pulsevoltage and the fuel flow rate is regulated by varying the duty ratio ofthe pulse voltage so as to regulate the effective value of the drivingcurrent supplied to the solenoid.

In the so-configured solenoid proportional control valve, however,static and dynamic friction arises between the piston and cylinderduring operation, and the hysteresis produced in the movement of thepiston by this mechanical operating friction causes a decline in theresponsivity of the valve system, deviation in the controlled flow rateand other effects that create a problem by making it impossible toconduct the flow rate control stably.

An object of the present invention is to provide a method and apparatusfor driving a solenoid proportional control valve utilized for flow ratecontrol that can overcome the aforesaid problem of the prior art.

Another object of the present invention is to provide a method andapparatus for driving a solenoid proportional control valve utilized forflow rate control that can realize stable flow rate control.

Another object of the present invention is to provide a method andapparatus for driving a solenoid proportional control valve utilized forflow rate control that can realize stable flow rate control withoutincreasing cost or electric power consumption.

DISCLOSURE OF THE INVENTION

The present invention is characterized in the point that

-   -   in a method for driving a solenoid proportional control valve        utilized for flow rate control, which regulates flow rate by        regulating a duty ratio of a pulse voltage applied to a coil of        a drive solenoid to control drive current flowing through the        coil,    -   electrical energy imparted to the coil is temporarily increased        at appropriate time points to instantaneously boost the driving        force of the drive solenoid.

The driving force of the drive solenoid can be instantaneously boostedeither by temporarily increasing the peak value of the pulse voltage atan appropriate time point or by conducting temporary increase of thepeak value of the pulse voltage repeatedly.

Whether or not an operating condition liable to cause hysteresis in theoperation of the solenoid proportional control valve utilized for flowrate control is present can be discriminated and the temporary increaseof the peak value of the pulse voltage be repeatedly conducted when itis discriminated that an operating condition liable to cause hysteresisin the operation of the solenoid proportional control valve is present.

The present invention is also characterized in the point that

-   -   in a method for driving a solenoid proportional control valve        utilized for flow rate control, which regulates flow rate by        regulating a duty ratio of a pulse voltage applied to a coil of        a drive solenoid to control drive current flowing through the        coil,    -   a pulse width of the pulse voltage is temporarily increased at        appropriate time points to instantaneously boost the driving        force of the drive solenoid.

The present invention is also characterized in the point that

-   -   an apparatus for driving a solenoid proportional control valve,        which is used to drive a solenoid proportional control valve        utilized for flow rate control, comprises:    -   means for supplying a prescribed frequency drive pulse voltage        of a duty ratio corresponding to a control signal supplied from        the outside to a coil of a drive solenoid of the solenoid        proportional control valve, and    -   means for temporarily increasing a pulse width of the drive        pulse voltage at appropriate time points.

The present invention is also characterized in the point that

-   -   an apparatus for driving a solenoid proportional control valve,        which is used to drive a solenoid proportional control valve        utilized for flow rate control, comprises:    -   means for supplying a prescribed frequency drive pulse voltage        of a duty ratio corresponding to a control signal supplied from        the outside to a coil of a drive solenoid of the solenoid        proportional control valve, and    -   means for temporarily increasing a pulse peak value of the drive        pulse voltage at appropriate time points.

The present invention is also characterized in the point that

-   -   in a method for driving a solenoid proportional control valve        utilized for flow rate control in a pump of a common rail system        adapted to regulate flow rate by regulating a duty ratio of a        pulse voltage applied to a coil of a drive solenoid to control        drive current flowing through the coil,    -   electrical energy imparted to the coil is temporarily increased        at appropriate time points to instantaneously boost the driving        force of the drive solenoid.

The present invention is also characterized in the point that

-   -   in a method for driving a solenoid proportional control valve        utilized for flow rate control in a pump of a common rail system        adapted to regulate flow rate by regulating a duty ratio of a        pulse voltage applied to a coil of a drive solenoid to control        drive current flowing through the coil,    -   a peak value of the pulse voltage is temporarily increased at        appropriate time points to instantaneously boost the driving        force of the drive solenoid.

The present invention is also characterized in the point that

-   -   in a method for driving a solenoid proportional control valve        utilized for flow rate control in a pump of a common rail system        adapted to regulate flow rate by regulating a duty ratio of a        pulse voltage applied to a coil of a drive solenoid to control        drive current flowing through the coil,    -   a pulse width of the pulse voltage is temporarily increased at        appropriate time points to instantaneously boost the driving        force of the drive solenoid.

The present invention is also characterized in the point that

-   -   an apparatus for driving a solenoid proportional control valve        used to drive a solenoid proportional control valve utilized for        flow rate control in a pump of a common rail system comprises:    -   means for supplying a prescribed frequency drive pulse voltage        of a duty ratio corresponding to a control signal supplied from        the outside to a coil of a drive solenoid of a solenoid        proportional control valve, and    -   means for temporarily increasing a pulse width of the drive        pulse voltage at appropriate time points.

The present invention is also characterized in the point that

-   -   an apparatus for driving a solenoid proportional control valve        used to drive a solenoid proportional control valve utilized for        flow rate control in a pump of a common rail system comprises:    -   means for supplying a prescribed frequency drive pulse voltage        of a duty ratio corresponding to a control signal supplied from        the outside to a coil of a drive solenoid of a solenoid        proportional control valve, and    -   means for temporarily increasing a pulse peak value of the drive        pulse voltage at appropriate time points.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an embodiment of the presentinvention.

FIG. 2 is a sectional view showing the detailed structure of a solenoidproportional control valve shown in FIG. 1.

FIG. 3 is an enlarged perspective view of a piston of the solenoidproportional control valve shown in FIG. 2.

FIG. 4 is a detailed circuit diagram of a drive control unit shown inFIG. 1.

FIG. 5 is a flow chart showing a control program executed in a CPU ofthe drive control unit shown in FIG. 4.

FIG. 6A is the waveform of a control output signal of the drive controlunit shown in FIG. 4.

FIG. 6B is a current waveform diagram of a solenoid coil drive signal ofthe drive control unit shown in FIG. 4.

FIG. 7 is the essential part of a flow chart for explaining amodification of the control shown in FIG. 5.

FIG. 8 is a circuit diagram showing a modification of the drive controlunit shown in FIG. 4.

FIG. 9 is a circuit diagram showing an example of the structure of adrive control unit for switching the voltage applied to a solenoid coilto conduct heavy current output processing.

FIG. 10 is a flow chart showing a control program executed in a CPU ofthe drive control unit shown in FIG. 9.

FIG. 11A is a waveform diagram of a control output signal of the drivecontrol unit shown in FIG. 9.

FIG. 11B is a current waveform diagram of a solenoid coil drive signalof the drive control unit shown in FIG. 9.

FIG. 12 is a circuit diagram showing a modification of the drive controlunit shown in FIG. 9.

FIG. 13 is a circuit diagram showing another modification of the drivecontrol unit shown in FIG. 9.

FIG. 14 is a circuit diagram showing another modification of the drivecontrol unit shown in FIG. 9.

BEST MODE OF CARRYING OUT THE INVENTION

In order to set out the present invention in greater detail, it will nowbe explained with reference to the attached drawings.

FIG. 1 is a block diagram showing an embodiment of the presentinvention. Illustrated here is the structure of an internal combustionengine fuel injection system configured using a solenoid proportionalcontrol valve drive apparatus according to the present invention. Thefuel injection system 1 is a common rail type fuel injection system thatuses multiple injectors 3 to inject high-pressure fuel accumulated in acommon rail 2 directly into corresponding cylinders of an internalcombustion engine not shown in the drawing. The system is configured tosupply the high-pressure fuel to the common rail 2 from a pump unit 4.

The pump unit 4 is configured to use a feed pump 41 to pump fuel 6 froma fuel tank 5 through an externally installed filter 7 to a pair ofhigh-pressure plungers 42, 43 driven by a drive section not shown in thedrawing. The configuration enables the flow rate of the fuel fed to thehigh-pressure plungers 42, 43 to be regulated by a solenoid proportionalcontrol valve 44 provided between the filter 7 and the high-pressureplungers 42, 43.

The fuel regulated in flow rate by the solenoid proportional controlvalve 44 is fed through check valves 45, 46 to the associatedhigh-pressure plungers 42, 43 where it is pressurized. The so-obtainedhigh-pressure fuel is fed to the common rail 2 through associated checkvalves 47, 48. Reference numeral 49 designates a return valve forreturning excess fuel on the delivery side of the feed pump 41 to thefuel tank 5. The structure of the pump unit 4 is known and thereforewill not be described in detail.

FIG. 2 is a sectional view showing the detailed structure of thesolenoid proportional control valve 44 shown in FIG. 1. The solenoidproportional control valve 44 has a cylindrical piston 44C open at oneend accommodated in a cylinder chamber 44Ba of a cylinder section 44Bprovided at one end of a casing 44A. The piston 44C is biased by spring44D toward a solenoid 44E provided in the casing 44A. As shown in detailin FIG. 3, the peripheral wall of the piston 44C is formed in itscircumferential direction with multiple, appropriately spaced slits44Ca.

An anchor 44Eb of the solenoid 44E operates in response to electricalcurrent flowing through a solenoid coil 44F to move the piston 44Cagainst the force of the spring 44D. The piston 44C is thereforepositioned at a location where the force of the spring 44D and thedriving force of the solenoid 44E determined by the magnitude of thecurrent flowing through the solenoid coil 44F are in equilibrium.

The cylinder section 44B is formed in the illustrated manner with fuelinlet ports 44Bb, 44Bb and a fuel outlet port 44Bc. The inlet ports44Bb, 44Bb communicate with an annular groove 44Bd formed inside thecylinder section 44B. The slits 44Ca and the annular groove 44Bd form anopen region when the piston 44C moves within the cylinder section 44B tobring the slits 44Ca opposite the annular groove 44Bd. The area of theopen region varies with the position of the piston 44C to substantiallyregulate the open areas of the inlet ports 44Bb, 44Bb, thereby enablingregulation of the flow rate of the fuel flowing from the inlet ports44Bb, 44Bb to the outlet port 44Bc.

Returning to FIG. 1, the fuel injection system 1 is equipped with adrive control unit 8, configured using a microcomputer, fordrive-controlling the solenoid proportional control valve 44 shown inFIG. 2. The drive control unit 8 is input with a rail pressure signal S1representing rail pressure from a rail pressure sensor 9 for detectingthe rail pressure, i.e., the fuel pressure in the common rail 2, a keyswitch ON signal S2 indicating that a key switch 10 is in the ONposition, an rpm signal S3 representing rotational speed from a rpmsensor 11 for detecting internal combustion engine speed, a temperaturesignal S4 representing fuel temperature from a temperature sensor 12 fordetecting the fuel temperature in the pump unit 4, and an acceleratorsignal S5 representing accelerator depression from an accelerator sensor13 for detecting the amount of manipulation of an accelerator pedal notshown in the drawing.

The drive control unit 8 uses the input signals S1-S5 to calculate thecontrol amount of the solenoid proportional control valve 44 requiredfor obtaining a fuel flow rate suitable for the instantaneous operatingcondition.

FIG. 4 is a detailed diagram of the drive control unit 8 shown inFIG. 1. A central processing unit (CPU) 8B of a microcomputer 8Aprocesses the input signals S1-S5 in accordance with a control programexplained later and outputs a control output signal CS. The drivecontrol unit 8 is equipped with a drive circuit composed of a flywheeldiode 8C and a switching transistor 8D. The connection point between theflywheel diode 8C and switching transistor 8D is connected through adetection resistor 8E to one end of the solenoid coil 44F of thesolenoid proportional control valve 44 whose other end is connected to adc power supply +B.

The control output signal CS is a pulse voltage signal of prescribedfrequency for conducting duty ratio control of the ON/OFF operation ofthe switching transistor 8D by a pulse signal. The switching transistor8D turns ON and OFF in response to the control output signal CS so as toapply a pulse voltage corresponding to the control output signal CS tothe solenoid coil 44F. As a result, driving current corresponding to theduty ratio of the pulse voltage signal flows through the solenoid coil44F as a drive signal DS. A voltage amplifier 8F is responsive to avoltage signal Vd produced by current flowing through a detectionresistor 8E to produce and input to the microcomputer 8A a detectionsignal S6 representing the instantaneous magnitude of the drivingcurrent flowing through the solenoid coil 44F.

The control of the driving of the solenoid proportional control valve 44effected based on the input signals S1-S6 will now be explained withreference to FIG. 5. FIG. 5 is a flow chart showing a control programinstalled in the microcomputer 8A for drive-controlling the solenoidproportional control valve 44 and executed by the CPU 8B. When thiscontrol program is launched to commence its execution, first, in stepS11, a desired rail pressure Pt is calculated. The desired rail pressurePt is calculated based on the accelerator signal S5 and rpm signal S3.

Next, in step S12, a desired flow rate Ft of fuel in the solenoidproportional control valve 44 is calculated from the desired railpressure Pt and rail pressure signal S1. Then, in step S13, a desiredduty ratio DTt of the control output signal CS required for obtainingthe desired flow rate is calculated from the desired flow rate Ft anddetection signal S6.

In step S14, the desired duty ratio DTt obtained in step S13 iscorrected in accordance with the temperature signal S4, and in step S15,an energization duty ratio DTa is calculated based on the correctionresult in step S14.

Basically, a pulse voltage of prescribed frequency controlled in dutyratio in accordance with the energization duty ratio DTa is output asthe control output signal CS. However, when hysteresis is liable toarise in the movement of the piston 44C owing to operating friction atthe operating portion of the solenoid proportional control valve 44, adiscrimination is made in step S16 regarding the need to introduce heavycurrent into the solenoid coil 44F so as to temporarily increase theelectrical energy imparted to the solenoid coil 44F at appropriate timepoints and enable the driving force of the solenoid proportional controlvalve 44 by the control output signal CS to be instantaneously boosted.

The discrimination in step S16 is for determining whether or not a heavycurrent introduction condition is present. In this embodiment, thediscrimination is made regarding each of the five conditions of whetheror not: (1) engine starting in progress, (2) engine very cold, (3)engine temperature high, (4) engine in specified speed range, and (5)rail pressure deviation outside prescribed value for prescribed periodor longer. Presence of a heavy current introduction condition isdiscriminated when at least one of these conditions is present.Condition (1) is discriminated based on the key switch ON signal S2.Conditions (2) and (3) are discriminated based on the temperature signalS4. Condition (4) is discriminated based on the rpm signal S3. Condition(5) is discriminated from the result obtained in step S11 and the railpressure signal S1.

Under an operating condition posing little likelihood of hysteresisarising in the movement of the solenoid proportional control valve 44,the control result in step S16 is NO and the program goes to step S17,in which normal current output processing is executed to output thepulse voltage of prescribed frequency duty ratio controlled inaccordance with the energization duty ratio DTa obtained in step S15 asthe control output signal CS. The switching transistor 8D turns ON andOFF in response to the control output signal CS and the resulting pulsevoltage is applied to the solenoid coil 44F, whereby driving currentcorresponding to the energization duty ratio DTa flows pulse-likethrough the solenoid coil 44F of the solenoid proportional control valve44 as the drive signal DS to control the flow rate of fuel in thesolenoid proportional control valve 44 to the desired flow rate Ft.

When presence of a heavy current introduction condition isdiscriminated, on the other hand, the result in step S16 is YES and theprogram goes to step S18. In step S18, the parameters required for heavycurrent application are calculated based on the rail pressure signal S1.The calculation can be done also taking the engine coolant temperatureinto account. Since application of the heavy current is repeatedcyclically for a prescribed time in each cycle, a heavy currentapplication period p per cycle, a number of heavy current applications qper cycle, and a repetition cycle r are calculated.

In step S19, heavy current output processing is executed in accordancewith the results of the calculations in steps S15 and S18 so as to dutycontrol opening and closing of the solenoid proportional control valve44 basically using the pulse voltage of prescribed constant frequencyduty ratio controlled in accordance with the energization duty ratio DTabut while repeating q number of applications of heavy current during thecurrent application period p of each cycle r and outputting the controloutput signal CS in accordance with this processing.

FIG. 6A shows an example of the voltage waveform of the control outputsignal CS obtained by the processing in step S19. Output of two broadpulse voltages is repeated in the current application period p of eachcycle r, while during the remaining period s other than the currentapplication period p, narrow pulse voltages of a prescribed frequency inaccordance with the normal current output processing in step S17 areoutput at the energization duty ratio DTa obtained in step S15. As isclear from the foregoing explanation, the pulse width of the broad pulsevoltages for heavy current driving is determined by the currentapplication period p and the number of applications q.

FIG. 6B shows the current waveform of the drive signal DS when thecontrol output signal CS shown in FIG. 6A is applied to the switchingtransistor 8D as a gate voltage signal. During the current applicationperiods p, the application of the broad pulse voltages makes the timethe switching transistor 8D stays ON long to increase the level of thecurrent flowing through the solenoid coil 44F. The peak value Wp of thecurrent flowing through the solenoid coil 44F during the currentapplication periods p is therefore greater than the current peak valueWs when the narrow pulse voltages are applied during the periods s, sothat during the current application periods p a larger amount ofelectrical energy is applied to the solenoid coil 44F than during theperiods s, thereby driving the solenoid proportional control valve 44with larger driving force. In other words, the pulse width of the pulsevoltages is temporarily increased at appropriate time points torepeatedly carry out instantaneous boosting of the driving force of thedrive solenoid.

Therefore, when operating friction arises in the solenoid proportionalcontrol valve 44, the driving force is instantaneously boosted duringthe current application periods p to enable the piston 44C of thesolenoid proportional control valve 44 to overcome the operatingfriction and operate smoothly. Occurrence of degraded responsivity andcontrolled variable deviation in the solenoid proportional control valve44 as a valve device can therefore be effectively minimized to enablestable flow rate control.

In step S20, discrimination is made as to whether the absolute value ofthe difference ΔP obtained by subtracting the actual rail pressure Pafrom the desired rail pressure Pt is smaller than a prescribed value K.When the absolute value of the difference ΔP is smaller than theprescribed value K, this means that the solenoid proportional controlvalve 44 is operating smoothly. In such case, the discrimination resultin step S20 is YES and the program goes to step S17 to conduct normalcurrent output processing.

On the other hand, when the absolute value of the difference ΔP is equalto or greater than the prescribed value K, this means the solenoidproportional control valve 44 is not operating smoothly and heavycurrent output processing is still necessary. In such case, thediscrimination result in step S20 is NO and the program returns to stepS18. The execution of steps S18 and S19 is thus cyclically repeateduntil the absolute value of the difference ΔP becomes smaller than K.Alternatively, a program can be adopted that returns to step S19 whenthe discrimination result in step S20 is NO.

In the control shown in FIG. 5, the heavy current output processing isrepeated in accordance with the parameters decided in step S18 until thedifference ΔP becomes smaller than a prescribed value. Instead, however,it is possible to adopt a configuration wherein the parameters decidedin step S18 are changed to impart greater electrical energy when thedifference ΔP does not become smaller than the prescribed value K afterthe elapse of a prescribed time following the start of the heavy currentoutput processing.

FIG. 7 is the essential part of a flow chart for an embodiment of suchcontrol, which replaces the step S18-S20 portion of FIG. 5.

In FIG. 7, steps S21, S22 correspond to steps S18, S19, respectively. Atimer is started in step S23, whether or not the value T of the timer isequal to or greater than a prescribed value M is discriminated in stepS24, and when T<M, i.e., when the discrimination result is NO, theprogram goes to step S25. Step S25 corresponds to step S20 in FIG. 7 andwhen the discrimination result therein is YES, the program goes to stepS17. When the discrimination result in step S25 is NO, the programreturns to step S21 to repeat execution of steps S21-S25.

So long as the discrimination result in step S25 has not yet become YES,the discrimination result in step S24 becomes YES and the program goesto step S26 when T becomes equal to or greater than M (T≧M). In stepS26, parameters are calculated that cause greater electrical energy tobe applied than do the parameters calculated in step S21. For instance,the parameters are appropriately changed such as by increasing thevalues of p and q among the parameters p, q and r so as to prolong thecurrent application period p and increase the number of currentapplications q.

In step S27, heavy current output processing is executed in accordancewith the parameters calculated in step S26. The processing in step S27is basically the same as that in step S22, differing therefrom only inthat the magnitude of the electrical energy applied to the solenoid coil44F during each current application period p is greater than in stepS22.

In step S28, discrimination is made as to whether the absolute value ofthe difference ΔP obtained by subtracting the actual rail pressure Pafrom the desired rail pressure Pt is smaller than the prescribed valueK. When the absolute value of the difference ΔP is smaller than theprescribed value K, this means that the solenoid proportional controlvalve 44 is operating smoothly. In such case, the discrimination resultin step S28 is YES and the program goes to step S17 to conduct normalcurrent output processing.

On the other hand, when the absolute value of the difference ΔP is equalto or greater than the prescribed value K, this means the solenoidproportional control valve 44 is not operating smoothly and heavycurrent output processing is still necessary. In such case, thediscrimination result in step S28 is NO and the program returns to stepS26. The execution of steps S26 and S27 is thus repeated until theabsolute value of the difference ΔP becomes smaller than K.Alternatively, a program can be adopted that returns to step S27 whenthe discrimination result in step S28 is NO.

The configuration shown in FIG. 7 achieves smooth operation of thesolenoid proportional control valve 44 by using larger electrical energywhen the heavy current output processing in accordance with theparameters calculated in step S21 is ineffective even when continued fora certain period of time. As such, it enables smooth operation of thesolenoid proportional control valve 44 without putting a heavy burden onthe solenoid proportional control valve 44.

Although the circuit configuration exemplified in FIG. 4 uses theswitching transistor 8D as a low-side switch, it is possible instead touse the switching transistor 8D as a high-side switch.

FIG. 8 shows a circuit diagram in the case of using the switchingtransistor 8D as a high-side switch. The sections of the drive controlunit 81 shown in FIG. 8 that correspond to sections in FIG. 4 areassigned the same reference symbols as those in FIG. 4.

In the embodiment shown in FIG. 1, the heavy current output processingdoes not change the level of the voltage applied to the solenoid coil44F but expands the time period of voltage application to the solenoidcoil 44F so that the peak value Wp of the current flowing through thesolenoid coil 44F during a prescribed current application period pbecomes greater than the peak value Ws. However, it is also possible toadopt a configuration for the heavy current output processing in whichthe electrical energy applied to the solenoid coil 44A is increased byincreasing the level of the voltage applied to the solenoid coil 44Awithout expanding the time period of voltage application.

FIG. 9 is a circuit diagram of a drive control unit 82 with a circuitlayout used in such a configuration. In the drive control unit 82,sections that are the same as sections of the drive control unit 8 areassigned the same reference symbols as those in the drive control unit8. 82A is a step-up circuit for outputting a dc voltage VH higher thanpower supply voltage +B, and 82B is a switch for selectively applyingeither the power supply voltage +B or the dc voltage VH to the solenoidcoil 44F. The switch 82B opens and closes in response to a switchcontrol signal S7 from the microcomputer 8A. The dc voltage VH isapplied to the solenoid coil 44F when the switch 82B is open. When theswitch 82B is closed, a diode 82C is put in a reverse biased state andthe power supply voltage +B is applied to the solenoid coil 44F.

FIG. 10 is a flow chart showing a control program executed in the caseof using the drive control unit 82 shown in FIG. 9. Steps in the flowchart shown in FIG. 10 that are the same as steps in the flow chartshown in FIG. 5 are assigned the same reference symbols as those in FIG.5 and explanation thereof will be omitted. The flow chart shown in FIG.10 differs from that shown in FIG. 5 only in the step S31 forcalculating parameters for heavy current application.

When the control result in step S16 is YES, the program goes to stepS31, in which the current application period p and the number ofapplications q among the parameters are decided. Here, the controloutput signal CSa constituting the pulse voltage is given a constantperiod and the current application period p is automatically determinedby deciding the number of times q that the solenoid coil 44F is drivenby the high voltage VH. During the current application period p, controlis effected so as to output the switch control signal S7 and open theswitch 82B.

FIG. 11A shows an example of the voltage waveform of the control outputsignal CSa obtained by the processing in step S19. The case where q=4,i.e., where four pulses are output in each current application period p,is illustrated. During the current application period p, the switch 82Bis opened by the switch control signal S7 and the high voltage VH isapplied to the solenoid coil 44F.

FIG. 11B shows the current waveform of the drive signal DSa when thecontrol output signal CSa shown in FIG. 11A is applied to the switchingtransistor 8D as a gate voltage signal. Owing to the application of thehigh voltage VH, the ON time of the switching transistor 8D during thecurrent application periods p is the same as that during the periods s,but the peak value of the current flowing through the solenoid coil 44Fis increased. Since more electrical energy is therefore applied to thesolenoid coil 44F during the current application periods p than duringthe periods s, the solenoid proportional control valve 44 is driven withlarger driving force. In other words, the pulse width of the pulsevoltages is temporarily increased at appropriate time points torepeatedly carry out instantaneous boosting of the driving force of thedrive solenoid.

FIG. 12 shows a modification of the drive control unit 82 shown in FIG.9. The sections in FIG. 12 that correspond to sections in FIG. 9 areassigned the same reference symbols as those in FIG. 9. The drivecontrol unit 83 shown in FIG. 12 is configured to apply a high voltageVH from a high-voltage output circuit 83A to the solenoid coil 44Fthrough a switch 83B and to apply the power supply voltage +B to thesolenoid coil 44F through a diode 83C. The power supply voltage +B istherefore applied to the solenoid coil 44F when the switch 83B is open.When the switch 83B is closed, the diode 83C is put in a reverse biasedstate and the high voltage VH is applied to the solenoid coil 44F. Inthis case, therefore, the switch 83B is controlled by the switch controlsignal S7 to close only during the current application period p.

FIG. 13 shows another modification of the drive control unit 82 shown inFIG. 9. The sections in FIG. 13 that correspond to sections in FIG. 9are assigned the same reference symbols as those in FIG. 9. The drivecontrol unit 84 is provided between the switching transistor 8D and theflywheel diode 8C with a diode 84C required when the voltage applied tothe solenoid coil 44F is switched by a switch 84B. When the switch 84Bis open, the high voltage VH is supplied to the solenoid coil 44Fthrough the diode 84C, and when the switch 84B is closed, the diode 84Cis put in a reverse biased state and the power supply voltage +B isapplied to the solenoid coil 44F. In this case, therefore, the switch84B is controlled by the switch control signal S7 to open only duringthe current application period p.

FIG. 14 shows another modification of the drive control unit 82 shown inFIG. 9. The sections in FIG. 14 that correspond to sections in FIG. 9are assigned the same reference symbols as those in FIG. 9. The drivecontrol unit 85 is provided between the switching transistor 8D and theflywheel diode 8C with a diode 85C required when the voltage applied tothe solenoid coil 44F is switched by a switch 85B. When the switch 85Bis open, the power supply voltage +B is applied to the solenoid coil44F, and when the switch 84B is closed, the diode 84C is put in areverse biased state and the high voltage VH is applied to the solenoidcoil 44F. In this case, therefore, the switch 85B is controlled by theswitch control signal S7 to close only during the current applicationperiod p.

The foregoing embodiments were all explained regarding the case ofapplication to flow rate control of a common rail system pump. However,the present invention is not limited to the aforesaid embodiments butcan of course be similarly applied with similar effect to solenoidproportional valves utilized for flow rate control of various fluidsused for other purposes.

In accordance with the present invention, when static or dynamicfriction arises between the piston and cylinder of a solenoidproportional control valve used for flow rate control of a common railsystem pump, these frictional forces can be overcome to enable movementof the piston by temporarily increasing the electrical energy applied tothe coil of the drive solenoid thereof at appropriate time points.Occurrence of degraded responsivity, flow rate deviation and otherproblems as a valve device can therefore be effectively minimized toenable stable flow rate control.

Since the present invention is configured to temporarily increase theelectrical energy applied to the coil at appropriate time points, itlowers power consumption in comparison with the conventional method ofcontinuously passing heavy current through the coil from the initialdriving stage. In addition, it does not increase cost either on thesolenoid side or the drive side because there is no need to raise theelectrical rating to one capable of withstanding continuous applicationof heavy current.

Industrial Applicability

As set out in the foregoing, the method and apparatus for driving asolenoid proportional control valve utilized for flow rate controlaccording to the present invention enable stable flow rate control evenwhen friction arises between the piston and cylinder of a solenoidproportional control valve used for flow rate control and, as such, helpto provide an improved method and apparatus for driving a solenoidproportional control valve utilized for flow rate control.

1. A method for driving a solenoid proportional control valve utilizedfor flow rate control, which regulates flow rate by regulating a dutyratio of a pulse voltage applied to a coil of a drive solenoid tocontrol drive current flowing through the coil, characterized in that:electrical energy imparted to the coil is temporarily increased atappropriate time points to instantaneously boost a driving force of thedrive solenoid.
 2. A method for driving a solenoid proportional controlvalve utilized for flow rate control, which regulates flow rate byregulating a duty ratio of a pulse voltage applied to a coil of a drivesolenoid to control drive current flowing through the coil,characterized in that: a driving force of the drive solenoid isinstantaneously boosted by temporarily increasing a peak value of thepulse voltage at appropriate points.
 3. A method for driving a solenoidproportional control valve used for flow rate control as claimed inclaim 2, wherein the temporary increase of the peak value of the pulsevoltage is conducted repeatedly.
 4. A method for driving a solenoidproportional control valve used for flow rate control as claimed inclaim 2, wherein: whether or not an operating condition liable to causehysteresis in operation of the solenoid proportional control valveutilized for flow rate control is present is discriminated; and thetemporary increase of the peak value of the pulse voltage is repeatedlyconducted when it is discriminated that an operating condition liable tocause hysteresis in the operation of the solenoid proportional controlvalve is present.
 5. A method for driving a solenoid proportionalcontrol valve used for flow rate control as claimed in claim 2, wherein:the solenoid proportional control valve used for flow rate control isutilized for flow rate control in a pump of a common rail system; andrepetition of the temporary increase of the peak value of the pulsevoltage is discontinued when a difference between a desired value andactual value of common rail pressure assumes a prescribed state.
 6. Amethod for driving a solenoid proportional control valve utilized forflow rate control, which regulates flow rate by regulating a duty ratioof a pulse voltage applied to a coil of a drive solenoid to controldrive current flowing through the coil, characterized in that: a pulsewidth of the pulse voltage is temporarily increased at appropriate timepoints to instantaneously boost the driving force of the drive solenoid.7. A method for driving a solenoid proportional control valve used forflow rate control as claimed in claim 6, wherein the temporary increaseof the pulse width of the pulse voltage is conducted repeatedly.
 8. Amethod for driving a solenoid proportional control valve used for flowrate control as claimed in claim 6, wherein: whether or not an operatingcondition liable to cause hysteresis in operation of the solenoidproportional control valve utilized for flow rate control is present isdiscriminated; and the temporary increase of the pulse width of thepulse voltage is repeatedly conducted when it is discriminated that anoperating condition liable to cause hysteresis in the operation of thesolenoid proportional control valve is present.
 9. A method for drivinga solenoid proportional control valve used for flow rate control asclaimed in claim 7, wherein: the solenoid proportional control valveused for flow rate control is utilized for flow rate control in a pumpof a common rail system; and repetition of the temporary increase of apulse width of the pulse voltage is discontinued when a differencebetween a desired value and actual value of common rail pressure assumesa prescribed state.
 10. A method for driving a solenoid proportionalcontrol valve used for flow rate control as claimed in claim 1, wherein:the solenoid proportional control valve used for flow rate control isutilized for flow rate control in a pump of a common rail system; andthe electrical energy is further increased when a difference between adesired value and actual value of common rail pressure does not assume aprescribe state after elapse of a prescribed time period.
 11. Anapparatus for driving a solenoid proportional control valve, which isused to drive a solenoid proportional control valve utilized for flowrate control, comprising: means for supplying a prescribed frequencydrive pulse voltage of a duty ratio corresponding to a control signalsupplied from the outside to a coil of a drive solenoid of the solenoidproportional control valve; and means for temporarily increasing a pulsewidth of the drive pulse voltage at appropriate time points.
 12. Anapparatus for driving a solenoid proportional control valve, which isused to drive a solenoid proportional control valve utilized for flowrate control, comprising: means for supplying a prescribed frequencydrive pulse voltage of a duty ratio corresponding to a control signalsupplied from the outside to a coil of a drive solenoid of the solenoidproportional control valve; and means for temporarily increasing a pulsepeak value of the drive pulse voltage at appropriate time points.
 13. Amethod for driving a solenoid proportional control valve utilized forflow rate control in a pump of a common rail system adapted to regulateflow rate by regulating a duty ratio of a pulse voltage applied to acoil of a drive solenoid to control drive current flowing through thecoil, characterized in that: electrical energy imparted to the coil istemporarily increased at appropriate time points to instantaneouslyboost the driving force of the drive solenoid.
 14. A method for drivinga solenoid proportional control valve utilized for flow rate control ina pump of a common rail system adapted to regulate flow rate byregulating a duty ratio of a pulse voltage applied to a coil of a drivesolenoid to control drive current flowing through the coil,characterized in that: a peak value of the pulse voltage is temporarilyincreased at appropriate time points to instantaneously boost thedriving force of the drive solenoid
 15. A method for driving a solenoidproportional control valve utilized for flow rate control in a pump of acommon rail system adapted to regulate flow rate by regulating a dutyratio of a pulse voltage applied to a coil of a drive solenoid tocontrol drive current flowing through the coil, characterized in that: apulse width of the pulse voltage is temporarily increased at appropriatetime points to instantaneously boost the driving force of the drivesolenoid.
 16. An apparatus for driving a solenoid proportional controlvalve used to drive a solenoid proportional control valve utilized forflow rate control in a pump of a common rail system comprising: meansfor supplying a prescribed frequency drive pulse voltage of a duty ratiocorresponding to a control signal supplied from the outside to a coil ofa drive solenoid of a solenoid proportional control valve; and means fortemporarily increasing a pulse width of the drive pulse voltage atappropriate time points.
 17. An apparatus for driving a solenoidproportional control valve used to drive a solenoid proportional controlvalve utilized for flow rate control in a pump of a common rail systemcomprising: means for supplying a prescribed frequency drive pulsevoltage of a duty ratio corresponding to a control signal supplied fromthe outside to a coil of a drive solenoid of a solenoid proportionalcontrol valve; and means for temporarily increasing a pulse peak valueof the drive pulse voltage at appropriate points.